Wireless mobile communication technology uses various standards and protocols to transmit data between a node (e.g., a transmission station or a transceiver node) and a wireless device (e.g., a mobile device). Some wireless devices communicate using orthogonal frequency-division multiple access (OFDMA) in a downlink (DL) transmission and single carrier frequency division multiple access (SC-FDMA) in an uplink (UL) transmission. Standards and protocols that use orthogonal frequency division multiplexing (OFDM) for signal transmission include the third generation partnership project (3GPP) long term evolution (LTE), the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard (e.g., 802.16e, 802.16m), which is commonly known to industry groups as WiMAX (worldwide interoperability for microwave access), and the IEEE 802.11 standard, which is commonly known to industry groups as WiFi.
In 3GPP radio access network (RAN) LTE systems, the node can be a combination of evolved universal terrestrial radio access network (E-UTRAN) NodeBs (also commonly denoted as evolved NodeBs, enhanced NodeBs, eNodeBs, or eNBs) and radio network controllers (RNCs). The eNBs communicate with the wireless device, known as a user equipment (UE). The DL transmission can be a communication from the node (e.g., eNB) to the wireless device (e.g., UE), and the UL transmission can be a communication from the wireless device to the node.
In homogeneous networks, the node, also called a macro node, can provide basic wireless coverage to wireless devices in a cell. The cell can be the physical region or area inside which the wireless devices are operable to communicate with the macro node. Heterogeneous networks (HetNets) can be used to handle the increased traffic loads on the macro nodes due to the increased usage and functionality of wireless devices. HetNets can include a layer of planned high-power macro nodes (or macro-eNBs) overlaid with layers of lower power nodes (small-eNBs, micro-eNBs, pico-eNBs, femto-eNBs, or home eNBs (HeNBs)) that can be deployed in a less well-planned or even entirely uncoordinated manner within the coverage area (cell) of a macro node. The lower power nodes (LPNs) can generally be referred to as “low power nodes”, small nodes, or small cells.
The macro node can be used for basic coverage. The low power nodes can be used to fill coverage holes, to improve capacity in hot zones or at the boundaries between the macro nodes' coverage areas, and to improve indoor coverage where building structures impede signal transmission. Inter-cell interference coordination (ICIC) or enhanced ICIC (eICIC) may be used for resource coordination to reduce interference between the nodes, such as macro nodes and low power nodes, in a HetNet.
HetNets can use time-division duplexing (TDD) or frequency-division duplexing (FDD) for downlink or uplink transmissions. TDD is an application of time-division multiplexing (TDM) to separate downlink and uplink signals. In TDD, DL and UL signals may be carried on the same carrier frequency, where the DL signals use a different time interval from the UL signals. Thus, the DL signals and the UL signals do not generate interference with each other. TDM is a type of digital multiplexing in which two or more bit streams or signals, such as a DL or UL signal, are transferred apparently simultaneously as sub-channels in one communication channel, but are physically transmitted on different time resources. In FDD, a UL transmission and a DL transmission can operate using different frequency carriers. In FDD, interference can be avoided because the DL signals use a different frequency carrier from the UL signals.
Time-division duplexing (TDD) offers flexible deployments without requiring a pair of spectrum resources. Long-term evolution (LTE) TDD allows for asymmetric uplink-downlink (UL-DL) allocations by providing seven different semi-statically configured UL-DL frame configurations, described in more detail below. These predefined LTE frame configurations may include flexible subframes in which some of the subframes originally defined for uplink transmissions may be changed to downlink subframes.
Enhanced Interference Mitigation and Traffic Adaptation (eIMTA), also known as “dynamic TDD”, provides such enhancements to LTE TDD systems for more efficient DL-UL traffic management. Under eIMTA, the eNB is able to transmit downlink data using one of the uplink subframes of the radio frame. Thus, the radio frame balance between uplink and downlink allocations can be dynamically changed to meet the instantaneous traffic situation. Significant performance benefits can be obtained by allowing TDD UL-DL reconfiguration based on the instantaneous traffic conditions in small cells, as well as by considering interference mitigation scheme(s).
As the UE operates in a wireless neighborhood, the channel conditions change. This may be due to movement by the UE, the presence of buildings and vehicles in the line of sight of the UE, and other conditions such as, for example, interference from neighboring stations, etc. Channel state information (CSI) is data about the channel conditions and is provided to the eNB by the UE during wireless communication. CSI may include channel quality information (CQI), pre-coding matrix indication, rank indication, and other information about the wireless channel.
There are two CSI reporting modes defined in LTE: aperiodic and periodic. Aperiodic CSI reporting takes place when the eNB makes a request and the UE supplies the CSI report in the PUSCH channel. Support of both CSI reporting modes may be desirable to assess the different interference environment in regular subframes and flexible subframes.
For the aperiodic mode, according to the legacy system behavior, in order to trigger the CSI report for the flexible subframe, the eNB needs to send a UL grant with aperiodic report trigger on one of the flexible subframes. However, due to eIMTA-specific HARQ operation behavior and also considering joint operation with carrier aggregation (CA), coordinated multipoint transmission (CoMP), or a combination of these, it may not always be possible to send UL grants on flexible subframes and new methods for aperiodic CSI triggering need to be defined.
Thus, there is a continuing need for a method to overcome the shortcomings of the prior art.